In recent years, touch panels have been installed as input devices in display devices such as liquid crystal panels and electronic papers. Regarding the configuration of touch panels, various configurations such as a resistant film system, a surface acoustic wave system and an electrostatic capacitance system are known, and the electrostatic capacitance system is known to be a system in which multi-point touch operation is possible and increase in area can be easily achieved. For example, an electrostatic capacitance type touch panel in which ITO (indium tin oxide) is used as a transparent conductive material has been disclosed (see Information DISPLAY, Vol. 26, No. 3, pp. 16-21).
However, there are problems in that: indium, which is a raw material of ITO, is expensive, and there are limitations on stable supply of indium; the production cost is high because a vacuum process is required for the production of thin films; and ITO films are brittle and have poor bending resistance. Therefore, substitute substances such as metal nanowires, carbon nanotubes, PEDOT and polyaniline have also been suggested.
A conductive member having a conductive layer containing conductive fibers such as metal nanowires, carbon nanotubes, and complexes of carbon nanotubes and metals, has been proposed (see, for example, Japanese National-Phase Publication No. 2009-505358). The conductive member includes, on a base material, a conductive layer containing plural metal nanowires, and when a photocurable composition is incorporated as a matrix into the conductive layer, the conductive member can be easily processed into a conductive member having a conductive layer that contains a preferable conductive region and non-conductive region, by patterned exposure and development subsequent thereto.
As a different mode of the conductive member containing conductive fibers as described above, a conductive member having a conductive layer that includes a preferable conductive region and non-conductive region can be easily processed by a method of incorporating a non-photocurable composition as a matrix into a conductive layer, performing drying and/or optionally crosslinking by a condensation reaction or a polymerization reaction to form a conductive layer, subsequently further forming a resist layer imagewise as an upper layer to the conductive layer using an etching resist or the like, and then performing an etching treatment; a method of partially disconnecting the conductive network in a uniformly formed transparent conductive layer by irradiation of laser light; or the like (see, for example, Japanese National-Phase Publication No. 2010-507199 and Japanese Patent Application Laid-Open (JP-A) No. 2010-44968).
Furthermore, as still another mode of the conductive member containing conductive fibers as described above, there has also been proposed a conductive layer-transferable conductive member in which a conductive layer containing conductive fibers is formed on a provisional support, the conductive layer is transferred to a glass substrate or the like, and then patterning by a photolithographic method or the like is optionally performed (see, for example, JP-A Nos. 2006-35771 and 2009-251186).
Regarding the conductive fibers that are preferably used in the conductive members described above, various materials are known, such as metal nanowires and nanorods of silver, gold, copper or the like; and carbon nanotubes, carbon nanorods, and composites of carbon nanotubes and a metal. Among them, it is known that metal conductive fibers fainted from a metal such as silver, gold or copper more preferably provide an excellent conductive member having low resistance and high transparency, and silver nanowires that are excellent in the balance among low resistance properties, durability and cost, are particularly preferably used.
However, there are cases in which, when a conductive member using such metal conductive fibers are exposed, for a long time, to harsh conditions such as high temperature conditions, high humidity conditions or the presence of ozone, an increase in resistivity that is speculated to be attributable to oxidation or morphological change of the metal may occur, and there are cases in which, depending on the application, an improvement of weather resistance is demanded.
Regarding the method for enhancing weather resistance of a transparent conductive material containing metal conductive fibers, methods of using a metal adsorbing compound having a specific structure have been disclosed (see, for example, Japanese National-Phase Publication No. 2009-505358 and JP-A No. 2009-146678). The method exhibits effectiveness depending on specific storage conditions, but there have been cases in which, since a metal adsorbing compound exhibits strong adsorptive property to metal conductive fibers, problems occur such as in that deterioration of conductivity or transparency of the conductive layer may occur, as aggregation of the metal conductive fibers occurs at the time of production of a transparent conductive material to deteriorate homogeneity of the conductive layer; and in that contact resistance between metal conductive fibers is increased whereby conductivity of the conductive layer is decreased.
Regarding a method for producing an aqueous dispersion containing metal nanowires, a method of adding a metal complex solution or a metal ion solution into an aqueous solvent containing a halogen compound and a reducing agent, has been disclosed (see, for example, JP-A No. 2010-84173). In the producing method, a desalting treatment is preferably carried out for the purpose of increasing the purity of the metal nanowires, and it is speculated that, when a desalting (washing) treatment disclosed in the Examples section is carried out, most of the reducing agent that did not contribute to the formation of the metal nanowires is eliminated. JP-A No. 2010-84173 has no description that the reducing agent that has been added at the time of reducing the metal complex intentionally remains, nor of effects thereof.
As discussed above, stable maintenance of the conductivity of a transparent conductive material containing metal conductive fibers even under harsh conditions such as high temperature conditions, high humidity conditions or the presence of ozone has not been sufficiently achieved with the related art, and there has been a demand for an improvement in weather resistance.